Can Regional Variations in Demographic Structure Explain Regional Differences in Car Use? A Case Study in Austria

Due to its manifold impact on the environment private car use represents an important dimension of environmental behavior in industrialized countries. Obviously, private car use is related to demographic characteristics of households such as the life-cycle stage and the living arrangement the household lives in. In addition systematic regional differences of private car use have to be taken into account. In this paper a causal model is derived, which aims to explain regional differences in car ownership and car use by regional demographic differences and region-specific control factors such as the car technology and institutional factors. Using aggregate data from a household survey in Austria and data from Austrian official statistics causal effect coefficients are then estimated. By applying path analysis the estimated effects of regional demographic characteristics on region-specific car ownership and car use can be decomposed into direct and indirect effects, with the latter effects being mediated by the control factors. Except for the average age of household heads and population density no significant direct demographic effects on regional patterns of car ownership and car use can be found. Car ownership and car use are best predicted by using the considered control factors as predictor variables. Nevertheless, many of the presumed indirect effects turn out to be of importance since demographic factors are closely linked to measures of regional institutional settings like per capita income, ownership of house/apartment and net commuting index.     

The effects and limits of territoriality on population regulation in grey red-backed voles,Clethrionomys rufocanus bedfordiae

Summary The effects of breeding territoriality on the stability of grey red-backed vole (Clethrionomys rufocanus bedfordiae) populations were investigated on a control grid and a grid on which the voles were fed, in an outdoor enclosure in Hokkaido, Japan. Vole populations were monitored by live trapping from 1984 to 1986: (1) Population density was 2–7 times greater on the experimental grid to which food was added than on the control grid. Reproductive output was more closely associated with the difference in density between grids than survival or dispersal (immigration and emigration) rates. (2) The number of adult females and pregnancy rate of the experimental population were significantly greater than those of the control one. The difference in the number of adult females between the populations was greater than that in pregnancy rate. (3) The proportion of successful litters and the number of weanlings per litter were not significantly different between the control and experimental population. (4) Adult females held territories on both the control and experimental grid; they were spaced out more than would be expected from random occupation. The territories overlapped more on the experimental grid than on the control grid. (5) Mean territory size of adult females on the experimental grid was about half of that on the control grid. The territory size was correlated negatively with population density. (6) The proportion of trap sites that were used by adult females was significantly greater on the experimental grid than on the control grid. This suggests that adult females on the experimental grid used the area more extensively. This factor, in association with territory size and overlapping of territory, was also important in causing the difference in the number of adult females between the grids. (7) These results call into question the hypothesis that territoriality stabilizes the density in populations ofClethrionomys.     

Effects on pregnancy outcomes of changes in the North Carolina State Abortion Fund

Extending work of Cook et al. (1999, 1996), this paper examines abortion funding cutoffs for poor women in North Carolina, a unique setting allowing for a strong quasi-experimental design. Using vital registration data and additional administrative data from North Carolina, we decompose program effects on the abortion/birth ratio into two components: coverage (i.e., the proportion of all abortions that are state funded) and substitutability (the proportion of state funded abortions that would have been births in the absence of the state program). We show that both components are crucial for understanding the effects of fund cutoffs and that both components vary by age and by race. We offer explanations for these differences. Overall, we conclude that: the North Carolina State Abortion Fund (SAF) had powerful and pervasive effects: i.e., the SAF cutoffs reduced abortions and increased births.     

Analysis of changes of insect-plant ratio-improvement of key-factor analysis for evaluating bottom-up effects in insect population dynamics

A revised key-factor analysis was presented for analyzing the temporal changes in the ratio of insect absolute number to plant resource. Ten data sets for 5 insect species were then analyzed. In this key-factor analysis, the key factor is defined as the factor contributing highly to between-year variation inR _r , the log rate of the inter-year change of the insect-plant ratio. The yearly change of plant resource was handled as a separate factor, expressed byr _pl , log ratio of plant resource in yearn to plant resource in yearn+1. The following was revealed: 1) In 7 of the 10 data sets examined,r _pl influenced variations ofR _r ; in particular in 3 casesr _pl was the main key factor. 2) Generation-to-generation fluctuations of absolute insect densities showed density dependence in 4 cases, while those of insect-plant ratios, in 8 cases. 3) The Royama model or a linear model, explained well the relationship between log insect-plant ratio (X _r ) andR _r and the relationship betweenX _r and log yearly change rate of absolute insect density (R _abs ). However, in the 7 cases in whichr _pl was a critical factor for variations ofR _r , with, increase ofX _r ,R _r showed a steeper, decrease around the equilibrium point (the point for whichR _r is 0) thanR _abs . This occurred becauser _pl tended to be negatively correlated withX _r . Consequently, in two casesX _r fluctuated cyclicly or chaotically although without the changes in plant resource, fluctuations ofX _r would be damped oscillations approaching equilibrium.     

The exponential multidimensional demographic projection model

This paper presents the multidimensional demographic projection on the basis of an exponential specification, which avoids the problems associated with the widely used specification on the basis of the linear integration hypothesis. It generalizes earlier work by Gill (1986) on Markov models for closed populations to include the case of open populations. A numerical illustration is also provided.     

Loss of genetic variability in a fragmented continuously distributed population

An individual-based simulation model was used to examine the effect of population subdivision, dispersal distance of offspring, and migration rates between subpopulations on genetic variability(H ₁ H _S andH _T ) in a continuously distributed population. Some difficulties with mathematical models of a continuously distributed population have been pointed out. The individual-based model can avoid these difficulties and can be used to examine genetic variability in a population within which individuals are distributed continuously and in which the dispersal of individuals is disturbed by geographical or artificial barriers. The present simulation showed that the pattern of decrease inH ₁ had three stages. During the first stage,H ₁ decreased at the rates predicted by Wright’s neighborhood size. During the second stage,H ₁ decreased more rapidly when the migration rate decreased, while during the third stage, it decreased less rapidly when the migration rate decreased. Increasing the number of subdivisions increased the rate of decrease after the 200th generation. The pattern of decrease inH _T was classified into 2 stages. During the first stage, the rates of decrease corresponded with those of a randomly mating population. During the second stage, a decrease in the migration rates of the subpopulations slowed the rate of decrease inH _T . A uniform spatial distribution and a reduced total dispersal distance of offspring causedH ₁ H _S , andH _T to decrease more rapidly. Habitat fragmentation in a continuously distributed population usually was detrimental to the genetic variability in the early generations. Other implications of the results for conservation are discussed.     

Dynamics of buried seed population and seedling cohorts of two dominant weeds in a hill agroecosystem of the humid subtropics of India

Dynamics of the buried seeds and plant population of two dominant weeds, viz.,Emilia sonchifolia (Linn.) DC. andRichardsonia pilosa HBK were studied in the crop fields of Meghalaya, north-east India during radish and maize cropping and intervening fallow periods. The total buried seed population ofR. pilosa was always larger than that ofE. sonchifolia, but the germinable fraction was invariably greater in the latter. A major portion (39–41%) of the viable (germinable+dormant) seed population in both weeds was confined to the surface soil layer (0–5 cm). The viable seed population ofE. sonchifolia peaked during April, while that ofR. pilosa showed two peaks (during August and December). The survival pattern and half-lives of seedling cohorts showed, some differences in the two weed species, but both being summer annuals, their populations behaved in a similar manner by showing higher seedling recruitment (K) and survivorship (p) rates in the summer crop (maize) than in the winter crop (radish). However, the density of plants that could attain adulthood was significantly higher inE. sonchifolia thanR. pilosa which might have resulted in greater seed input of the former to the soil leading to its greater abundance in the crop fields. Supported by the University Grants Commission, New Delhi (Grants No. F. 3-37/87 SR II)     

On the stability of the stock-harvesting system controlled by a feedback management procedure

Summary Stability of the stock-harvesting system regulated by a feedback control procedure of catch quota is examined. In the procedure considered, catch quota is changed proportionally to the difference between current and the target stock level (with a proportionality constanth) and to the annual stock growth rate (with a proportionality constantg). Condition for the local stability of the target equilibrium is obtained as a function of the stock-recruitment relation, survival probability of adults, target stock level, time lag before implementation of regulation, age of sexual maturity of the stock, and proportionality constantsg andh. It is shown that, (1) the procedure has the stabilizing effect; it can stabilize the target stock level that is unstable under constant harvest, (2) lower target stock level favors largerg and smallerh, when the target is set around MSYL (the stock level that gives MSY), (3) the degree of stability, measured by the time required to recover the target stock level, is an increasing function of the target stock level, (4) stability and sustainable yield are in trade-off, (5) time delay caused by the time needed before sexual maturity does not affect the stability significantly, but the effect of the time lag before implementation of regulation is significant. Comparison between harvest-control and effort-control procedures is also made, and the advantage of the latter in terms of stability is shown.     

世界人口格局中的中国人口转变及其特点

20世纪 50年代以后的中国人口转变与西方传统人口转变有许多不同之处 ,具有自身的特点 ,即转变的迅速性、控制干预性、不彻底性、不稳定性、不平衡性。把握新时期稳定低生育水平的决定是将我国人口转变进行到底的重要措施和手段 ,是实现人口可持续发展的重要步骤     

A population dynamic model of Batesian mimicry

Summary A population dynamic model of Batesian mimicry, in which populations of both model and mimetic species were considered, was analyzed. The probability of a predator catching prey on each encouter was assumed to depend on the frequency of the mimic. The change in population size of each species was considered to have two components, growth at the intrinsic growth rate and carrying capacity, and reduction by predation. For simplicity in the analyses, three assumptions were made concerning the carrying capacities of each population: (1) with no density effects on the mimic population growth rate; (2) with no density effects on the model species; and (3) with density effects on both species. The first and second cases were solved analytically, whereas the last was, for the most part, investigated numerically. Under assumption (1), two stable equilibria are possible, in which both species either coexist or go to extinction. Under assumption (2), there are also two stable equilibria possible, in which either only the mimic persists or both go to extinction. These results explain the field records of butterflies (Pachliopta aristolochiae and its mimicPapilio polytes) in the Ryukyu Islands, Japan.     

The momentum of mortality change

Mortality change is not usually assigned much importance as a source of population growth when future population trends are discussed. Yet it can make a significant contribution to population momentum. In populations that have experienced mortality change, cohort survivorship will continue varying for some time even if period mortality rates become constant. This continuing change in cohort survivorship can create a significant degree of mortality-induced population change, a process we call the ‘momentum of mortality change’. The momentum of mortality change can be estimated by taking the ratio of e ₀ (the period life expectancy at birth) to CAL (the cross-sectional average length of life) for a given year. In industrialized nations, the momentum of mortality change can attenuate the negative effect on population growth of declining fertility or sustained below-replacement fertility. In India, where population momentum has a value of 1.436, the momentum of mortality change is the greatest contributor to its value.     

建国以来新疆人口的省际迁移状况分析

新疆人口总数中。省际迁移人口占有重要的地位。文章分析了建国以来新疆人口迁移特点,结果表明：新疆人口迁移活动主要表征为国家有计划的迁移和人口自发迁移。迁移过程具明显的时间阶段性;迁入人口以文化素质较低的农村男性青壮年为主：人口迁入地区主要为开发程度高、经济发展快、交通便利的地区;人口迁入主因是国家政策及大量土地资源的吸引．人口迁出主因是区域经济发展不平衡、产业结构调整,祖籍亲缘关系、户籍管制的放松;省际人口迁移促进了新疆的经济发展以及新疆与其他省区的交流,但同时也带来了一些不刺影响。     

Biodiversity decline and population externalities

To understand the problem of the global biodiversity decline, we set up a north–south model of population and income determination. Although biodiversity decline is mainly caused by primitive agricultural activities in some poor countries, we show that policies of resource management or Pigouvian taxes, targeted solely at rectifying such activities, are often ineffective. Since the production activities in these poor countries are correlated with parents’ fertility decisions, any efficient rectifications must involve a change in parents’ reproduction choice as well. Responsible editor: Junsen Zhang     

城市流动人口计划生育管理的社区服务模式

我国目前对流动人口实行的防范式行政管理方法,在实际中不易落实,且易引起流动人口的排斥抵触情绪。因此必须针对流动人口的特点,采用计生社区服务模式为主的工作方式,转交流动人口的传统生育观。流动人口计生社区服务模式应着重:以经常性的宣传教育服务为宗旨;以生产、生活、生育服务为主线;注重社区服务的福利性质;以促进城市居民与流动人口沟通为目的。流动人口计生社区服务对于流动人口本身和社区计划生育而言具有很多优势,是以后流动人口计划生育管理服务的发展方向。     

Food limitation of population density in the orb-wed spider,Nephila clavata

Summary Field studies were conducted to clarify whether variation in food availability among habitats influences population density, and whether population density has a negative effect on foraging success in the orb-web spider,Nephila clavata. Lifetime food consumption per individual (i.e., foraging success) strongly correlated with mean body size of adult females and mean fecundity in populations. Also, there was a positive correlation between foraging success and population density. Since foraging success reflected potential prey availability in the habitat, food resource appeared to be a limiting factor for populations in this spider. Mean fecundity per individual correlated with population density of the following year, suggesting that decreased reproduction is a major component of food limitation on population density. Consistent defferences in mean body size between particular sites were observed over years, while such difference was less obvious in density. Thus, ranking of food abundance among habitats seems to be predictable between years. A field experiment revealed that an artificial increase in population density had no negative effect on the feeding rate of individuals, suggesting that intraspecific competition for food is not important in this species.     

Estimation of population size and survival of sheep blowfly,Lucilia cuprina, in the field from serial recoveries of marked flies affected by weather dispersal and age-dependent trappability

Summary A model is presented for analysis of mark-recapture data of mobile insects which, unlike the Lincoln Index, does not require marked individuals to remain within the sampling area or to mix uniformly with the wild population. The model assumes a single or multiple releases of marked insects from the centre of the sampling area and that captured individuals are not returned to the population. Dispersal rates of marked insects are estimable from serial recaptures and, for catches that are either unaffected by or have been corrected for weather effects, the model also provides estimates of mortality and age-dependent trappability. Application of the model is illustrated using mark-recapture data for adults of the Australian sheep blowflyLucilia cuprina. A Biometrics Unit report detailing all source data, program code and comparisons between dispersal models is available on request from the authors.     

Contest competition inDrosophila subobscura

The role of larval intraspecific competition in laboratory populations ofDrosophila subobscura was investigated. Mortality is density-independent during the first 3 days after hatching but becomes density dependent as development proceeds to pupation. Although total biomass per patch was independent of initial egg density, competition betweenDrosophila larvae leads to the formation of smaller pupae. This resulted in a population that was dominated by suppressed individuals. Development rate ofD. subobscura larvae was not affected by high larval densities. Smaller pupae give rise to females with fewer eggs in their ovarioles. A simple simulation model, predicting the effects of intraspecific competition on the fecundity of the nextDrosophila generation is described.     

Population dynamics of the whitebacked planthopper,Sogatella furcifera (Hemiptera: Delphacidae) with special reference to the relationship between its population growth and the growth stage of rice plants

A population census was conducted to describe the effects of the growth stage of rice on the population dynamics ofS. furcifera, in particular, on immigration, seasonal abundance, population growth rate, and wing-form expression. The number of immigrants was highest on rice plants 17 to 30 days after transplanting (DAT), which suggested that immigrants prefer to settle or remain more on rice plants at the tillering stage (approximately 20–30 DAT). Population growth rate from immigration to the 1st generation decreased with an increase in rice plant age. In contrast, population growth rate from the 1st to 2nd generation was not influenced by rice plant age and was negatively density-dependent. The percentage of macropters (flyers) was positively related to the growth stage of rice when rice was in the vegetative or early part of the reproductive stage, and reached 100% at about 10 days before heading (booting stage). Threafter, most adult females molted into macropters regardless of population density. The roles of host plant age and crowding effect on the population dynamics ofS. furcifera are discussed.     

Modelling selection for resistance to methods of insect pest control in combination

The development of resistance to insecticides is now widespread among insects. Other methods of pest control are also potentially at risk of encountering resistance. A modelling approach is presented here to evaluate the effects of combining methods of insect pest control on the selection for resistance to the control methods. This analysis is based on partitioning the total mortality acting on a population into its constituent components from all known sources, and these are related to selection for resistance. When two control methods are used in combination, selection for resistance against the two is a linear function if the two don't interact, otherwise it may be sublinear or supralinear. A specific example is presented using a model of the Olive fruit fly (Dacus oleae Gmel.) and employing food-baited and pheromone-baited traps for control. The control methods that appear least likely to encounter resistance are natural enemies and the use of pheromone traps for male annihilation. These should be integrated into a control program where possible to minimize the development of resistance to other control methods being used.     

The population dynamics of the voleClethrionomys rufocanus in Hokkaido, Japan

Population dynamics of the gray sided-vole,Clethrionomys rufocanus, in Hokkaido, Japan were described on the basis of 225 time series (being from 12 to 31 years long); 194 of the time series have a length of 23 years or longer. The time series were classified into 11 groups according to geographic proximity and topographic characteristics of the island of Hokkaido. Mean abundance varied among populations from 1.07 to 21.07 individuals per 150 trap-nights. The index of variability for population fluctuation (s-index) ranged from 0.204 to 0.629. Another index for population variability (amplitude on log-10 scale) ranged from 0.811 to 2.743. Mean abundance and variability of populations were higher in the more northern and eastern regions of the island. Most populations, except for the southernmost populations, exhibited significant direct density-dependence in population growth. Detection rate for delayed density-dependence varied among groups from 0% to 22.6%. Both direct and delayed density-dependence tended to be stronger in the more northern and eastern populations. The proportion of cyclic populations was higher in the northern-eastern areas than that in the southern-western areas. There was a clear gradient from the asynchronous populations in southwest, to the highly synchronized populations in the northeast.